Recent data from the WMAP (Wilkinson Microwave Anisotropy Probe) satellite
has shown that the observed cosmic microwave background has a spectral index
significantly lower than that predicted by most inflation models. This is true
in the case of supersymmetric (SUSY) hybrid inflation models, which are regarded
as a strongly favoured class of inflation model. A possible interpretation of
this discrepancy is that it is due to the influence of other particles. Together
with my student Chia-Min Lin, I have been investigating the effect of MSSM flat
direction fields (in particular right-handed [RH] sneutrinos) on SUSY hybrid
inflation models. We have established that the spectral index can naturally be
lowered to be consistent with WMAP observations. Future research aimed at
understanding the effect of such fields on the cosmic string density produced at
the end of inflation, which is typically too large in conventional SUSY hybrid
inflation models.

A longer-term research programme is the investigation of reheating in SUSY
inflation models. An important feature of inflation models is the process by
which they transit from the cold inflationary era to the standard hot Big Bang
model, known as reheating. In SUSY hybrid inflation models this is a complex
process of non-linear scalar field dynamics known as tachyonic preheating.
Understanding in detail how this process completes is a long-term research goal.
In addition, there have recently been significant developments in the physics of
reheating and gravitino production in supergravity models. Future research will
investigate reheating and gravitino production in a variety of supersymmetric
models with different supersymmetry-breaking mechanisms. A collaboration with
Helsinki University has recently been established to study these issues.

(ii) Dark Sector in Supersymmetric Models:

Only about 4% of the matter in the Universe corresponds to conventional
atomic (baryonic) matter. 23% is in the form of dark matter which clusters to
form the framework of galaxy formation. The remaining 73% is in the form of
'dark energy', which is responsible for the recent acceleration of the expansion
of the Universe. Dark matter plus dark energy collectively form the 'dark
sector'.

Supersymmetric particle physics theories provide natural candidates for dark
matter. In order to prevent rapid decay of the proton, a symmetry known as
R-parity [exact or weakly-broken] must be imposed. A side-effect of R-parity is
that the Lightest Supersymmetric Particle (LSP) is absolutely stable. This
provides a natural candidate for the dark matter particle. In particular, in the
case of neutralino dark matter, the thermal relic density left over after the
Big-Bang can have the right magnitude to naturally account for the observed dark
matter. However, other candidates for dark matter exist, with different
production mechanisms, including gravitinos, axinos, and RH sneutrinos.

One way to distinguish between DM candidiates is via their ability to account
for the baryon-to-dark matter (BDM) ratio. Observation has shown that the ratio
of the density in baryons to that in dark matter is about 1/6. However, the
production mechanisms for baryons and dark matter are usually physically
unrelated. It is therefore remarkable that their densities can be within an
order of magnitude. A natural interpretation of this observation is that the
dark matter and baryon densities have a similar cosmological origin. Requiring
that the baryon asymmetry and the dark matter density have a related origin
would provide a powerful principle by which to identify the correct particle
physics theory, baryogenesis mechanism and dark matter particle. This knowledge
would, in turn, allow us to probe more deeply into early Universe cosmology.

I have recently proposed that the BDM ratio can be explained by a dark matter
condensate of RH sneutrinos combined with a baryon asymmetry generated via
Affleck-Dine leptogenesis. In this model the densities of dark matter and
baryons both originate from Bose-Einstein condensates of scalar particles which
have closely related dynamics in the early Universe. Future research in this
area will aim to understand in detail the phenomenology and cosmology of RH
sneutrino dark matter, in particular the observational consequences for the CERN
Large Hadron Collider (LHC) and ESA Planck cosmic microwave background
satellite. In addition, alternative BDM scenarios and non-BDM dark matter models
will be explored in order to assess the uniqueness of the RH sneutrino BDM
model.

A complete description of the Dark Sector also requires an explanation of the
dark energy and why its density is similar to that of dark matter, a feature
known as the Coincidence Problem. This is particularly challanging in
supersymmetric models due to the large mass of the scalar particles in
supersymmetry. A long-term goal will be to investigate supersymmetric dark
energy models which can address the Coincidence Problem.

Teaching

I am the manager of the Physics with Astrophysics and Cosmology degree
scheme. In 2007/8 I will be teaching the PHYS 213 (Maths II) and PHYS 461
(Cosmology III) courses and administering the PHYS 364 Cosmology Lab. I will
also supervise two PHYS 451 MPhys projects.